[Mongrel] problems with apache 2.2 proxying to mongrel cluster

Michael Kovacs kovacs at gmail.com
Tue Jan 2 17:35:08 EST 2007

So you are currently proactively restarting mongrel processes every  
30 minutes? I have yet to setup monit but have every intention of
doing so very soon, but the process of proactively restarting  
mongrels regardless of state isn't something I'd relish doing. I  
don't imagine
that's the common case. At least I hope not.


On Jan 2, 2007, at 1:59 PM, Shawn Hill wrote:

> I have the same problem.  People (including myself) use monit to  
> ensure processes don't freeze and some also set up scripts to  
> periodically restart individual mongrels (mine restart every 30  
> minutes.)
> My setup:
> Linux 2.6.18
> everything else is the same, except I upgraded mongrel (which had  
> no effect on the problem.)
> Appreciate suggestions from people who have encountered and  
> successfully resolved this issue.
> From: mongrel-users-bounces at rubyforge.org [mailto:mongrel-users- 
> bounces at rubyforge.org] On Behalf Of Michael Kovacs
> Sent: Tuesday, January 02, 2007 2:10 PM
> To: mongrel-users at rubyforge.org
> Subject: [Mongrel] problems with apache 2.2 proxying to mongrel  
> cluster
> Hi all,
> I've been having problems with the apache 2.2-mod_proxy_balancer- 
> mongrel setup.
> My setup is:
> CentOS 4.3
> apache 2.2.3 (compiled from source) with mod_proxy_balancer
> mysql 4.1
> ruby 1.8.4
> mongrel 0.3.14 (I know I need to update but I think this problem is  
> independent of the mongrel version)
> mongrel_cluster 0.2.0
> rails_machine 0.1.1
> I have apache setup as per Coda's configuration on his blog posting  
> from several months back.
> http://blog.codahale.com/2006/06/19/time-for-a-grown-up-server- 
> rails-mongrel-apache-capistrano-and-you/
> I have 4 mongrels in my cluster.
> Things work fine for periods of time but after several hours of  
> inactivity (I think 8 hours or so) I experience oddness where only  
> 1 of the 4 mongrels is properly
> responding. I end up getting a "500 internal server error" 3 out of  
> 4 requests as they round robin from mongrel to mongrel. There is  
> nothing in the production
> log file nor in the mongrel log. I've reproduced this problem on my  
> staging box as well as my production box.
> The last time I reproduced the problem I decided to run "top" and  
> see what's going on when I hit the server.
> Mongrel does receive every request but mysql is only active on the  
> 1 request that works. In the other mongrels it never spikes up in  
> CPU usage.
> Looking at the mysql process list revealed that all of the  
> processes had received the "sleep" command but one of the processes  
> is still
> working properly. I've played with connection timeouts other than  
> to set the timeout in my application's environment
> (ActiveRecord::Base.verification_timeout = 14400) as well as the  
> mysql interactive_timeout variable but it seems that all the  
> mongrels should work or they shouldn't. The fact that 1 out of 4  
> always works is rather puzzling to me.
> Trying a 'killall -USR1 mongrel_rails" to turn debug on simply  
> killed the 4 threads running mongrel. So now I'm running the  
> cluster in debug mode and am going to just let it sit there for  
> several hours until it happens again and hopefully get some idea of  
> where the breakdown is happening. I still think it has to be a  
> mysql connection timeout but again, the fact that 1 of the 4 always  
> works doesn't lend credence to the timeout theory.
> Has anyone experienced this phenomenon themselves?
> Thanks for any tips/pointers and thanks Zed for all your hard work  
> with mongrel.
> -Michael
> http://javathehutt.blogspot.com
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